Development of Carbon Nanotube Inks for Printed Electronics

Abstract

Single-walled carbon nanotubes (SWNTs) have excellent electronic, mechanical, and optical properties that make them promising materials for various applications. However, SWNT production methods produce a mixture of semiconducting and metallic species and non-SWNT impurities limiting their incorporation into devices. Among the different purification methods, conjugated polymer sorting has proven to be a scalable and cost-effective method. Conjugated polymers can easily be tuned to disperse SWNT species and obtain solubility in target solvents. They are multifunctional structures that enable the purification and extraction of specific SWNTs while simultaneously enhancing their processability. Therefore, they are suitable as purification methods for the fabrication of SWNT-based devices, particularly for printed electronics. However, the polymer backbone and the non-conductive side-chains negatively impacts the performance of SWNT devices by preventing good contact between the nanotubes. We first functionalized our polymer with thermally cleavable side-chains and demonstrated that the removal of the side-chains leads to a higher conductivity. We obtained stable dispersions in two green solvents compatible with inkjet printing. We also functionalized our polymer with photocleavable side-chains and showed efficient cleavage in solution. These investigations represent a proof-of-concept that could be used for the development of SWNT-based devices where the removal of the side-chains will improve the device performance. Lastly, we synthesized a fluorene-based polymer that contains a photocleavable ortho-nitrobenzylether unit and is functionalized with hydrophilic side-chains. We demonstrated the degradation of the polymer in organic and aqueous solvents. These investigations highlight the challenges of dispersing SWNTs in aqueous solvents using conjugated polymer.